Test CLIs

[mikegerber]

We would have caught #109 early if we had tests of the CLI.

[mikegerber]

Now we had a broken dinglehopper-line-dirs CLI because we didn't test it...

[mikegerber]

I've put the test files I've used for manual tests here for now: https://github.com/mikegerber/dinglehopper-test-files

This will need some integration in the future.